Paper manufacture



Patented Sept. 27, 1932 UNITED STATES PATENT OFFICE GEORGE A. RICHTER, FBERLIN, NEW HAMPSHIRE, ASSIGNOR TO BROWN COMPANY, OF BERLIN, NEWHAMPSHIRE, A CORPORATION OF MAINE PAPER MANUFACTURE No Drawing.Application filed May 24,

In the manufacture of some varieties of paper, it is customary practiceto obtain certain desired characteristics by incorporating finelydivided solids into the fiber stock or furnish from which the body ofthe'paper is made, or to coat the paper with compositions containingsuch solids. When the body of the paper contains the solids distributedthcrethrough, it is known as afilled or loaded paper, or if it carriessuch solids on its surface, it is termed a coated paper.

In accordance with the present inventlon, I employ pulverized cellulosefiber as a papermaking ingredient, as I have found that such a powdermay be used to great advantage for such purpose. Not only is thepulverlzed cellulose useful as an addition to the fiber stock or furnishfrom which the body of the paper is made, but also in compositions forcoating the paper. The present invention, therefore, comprehends themanufacture of paper containing such powder distributed throughout thebody of the paper and/or carried on its surface.

The pulverized cellulose of the present invention is prepared fromcellulose fiber of any suitable origin, preferably by mechanical meansin order to preserve the chemical constitution of the fiber. It isessential that the subdivision of the fiber should occur in the absenceof a substantial proportion of water, which not only tends to retardpulverization but also to hydrate or gelatinize the cellulose into aform quite different from that desired for the present purpose. In fact,it is preferable that the fiber be in a bone-dry condition during thepulverizing operation, as in such condition it is most brittle and lendsitself to subdivision with a minimum expenditure of power. The fiber maybe pulverized in impact machines, such as hammer mills or ball mills,which have been found to be admirably suited for carrying out thepulverizing operation, but any other suitable grinding, crushing, orcutting machines may be employed. When ball mills are used, the heatgenerated during grinding, particularly during the summer season, may besufiicient to cause a yellowing of the cellulose even when the fiberused as a raw material is of 1930. Serial No. 455,456.

high alpha cellulose content and comparat1vely free from components suchas beta and gamma celluloses, lignin, resins, etc., which tend to darkenunder heat. In such case, heat generated during the pulverizingoperatlon may be removed from the charge by dellverlng a current ofcomparatively cool air thereagainst or against the grinding surfacesdurmg the pulverizing operation. If there is trouble in maintaining abone-dry condition in the cellulose during the grinding, the charge maybe allowed to increase in temperature by frictional heat so as to avoidthe formation of rust or other impurities on such parts of the ball millas may be subject to oxidation or change in the presence of moist air.For example, the temperature of the charge may be allowed to increase to60 to 70 C. without material effect on the cellulose when using an ironball mill equipped w1th ron rods. Unless such temperature condlt ons aremaintained when using such pulverlzlng equipment, suflicient moisture isabsorbed by the cellulose from the atmosphere, particularly on a humidday, to cause a progressive rusting of the iron, which may socontaminate the cellulose as to impart a tan or even a brown colorthereto.

The fiber may be pulverized to various degrees of fineness, forinstance, to particles of a size of from 40 to 200 mesh, depending uponthe surface characteristics desired in the finished paper product. Whena comparatively rough surface known as an eggshell finish is desired,the cellulose fiber may be powdered to a particle size of 40 mesh orcoarser, but if a smooth surface or finish is desired, the fiber shouldbe reduced to parti cles preferably of impalpable fineness. When thepulverizing operation is carried out in a ball mill, it is possible,after a prescribed period of time, to reduce most of the fiber to agiven particle size, but the powdered product may contain a certainamount of powdered cellulose coarser than that desired. Ordinarily, thepowdered batch as a whole may be used, but in certain instances where itis desired to control accurately the characteristics of the finishedpaper, the powdered batch may be graded into portions of differentparticle size, as by siftin through wire cloths or sieves, by carrying othe finer particles from the coarser particles in a current of air, ofby floating off the finer par- 5 ticles in a stream of water deliveredinto an aqueous suspension of the powder. Any other methods used ingrading or classifying pulverulent materials such as paint-pig ments maybe applied to the pulverized cellulose.

Pulverized cellulose produced as hereinbe'fore described does not takeon a slim-y or slippery condition in water, even when an aqueoussuspension thereof is subjected to intensive mechanical action, as in abeater engine. In other words, a slurry prepared from the pulverizedcellulose is quite different from the so-called slow or highlygelatinized stocks produced by papermakers, as for the manufacture ofglassine papers. Even after prolonged suspension in water, thepulverized cellulose retains what appears to be a granular form notunlike that of the usual mineral fillers used in paper manufacture, butthe pulverized cellulose is not as dense as those fillers. It is hencereasonable to anticipate that the pulverized cellulose, when used inpapers behaves more nearly like a filler than highly gel tinizedcellulose, and such is the case. This property renders the pulverizedcellulose valuable for use in paper manufacture in llull of or alongwith the usual mineral filling or coating materials to produce effectsin the paper which are diflicult otherwise to obtain. For example, theincorporation of the pulverulent cellulose into the paper stock not onlyincreases the opacity of the resulting paper, but also enhances itsflatness or smoothness 40 of surface, particularly when the pulverulentcellulose is of impalpable fineness. The

pulverulent cellulose may therefore be used to control the opaquenessand flatness of the finished paper, which characteristics, particularlyin a stock containing no added fillers, have been dependent largely onthe extent to which the fiber has been hydrated or beaten. Thus, thegreater the degree of hydration of a fiber, the higher will be itstransparency when in paper form,this principle being attested to by theglassine papers obtained from highly hydrated cellulose fiber, and, onthe other hand, the papetrie and vellum papers obtained from lightlyhydrated cellulose fiber. By incorporating pulverulent cellulose into awell beaten stock, it is possible to realize the strength, formation,and other desirable characteristics of paper made from a well-hydratedfiber, with the opacity, softness, and other characteristics of papermade from a lightly hydrated fiber. The particular characteristicsattained in the finished paper may be varied, depending upon the degreeof hydration of the paper stock and the derivation and time ness ofparticle size of the pulverulent cellulose which is added thereto. Inany event, however, it is possible for a paper manufacturer, inaccordance with the present invention, to produce papers havingcharacteristics heretofore realized, if at all, by the use of mineralfillers,- without the use of such mineral fillers. These characteristicsare obtainable by the use of the same material, namely, cellulose, ofwhich the body of the paper is made, so that the paper manufacturer doesnot have to rely upon mineral materials which have sometimes beenclassified as'adulterants. The present invention, also, by dispensinwith the necessity for the use of mineral llers, further makes the papermanufacturer independent of control by those engaged in marketingmineral fillers,a raw material which most paper manufacturers mustobtain from outside sources.-

In producing papers filled or loaded with the pulverulent cellulose, theprocedure followed may be more or less analogous to that ofincorporating the usual mineral fillers. That is to say, the pulverulentcellulose may be added to the stock in the beater engine before or afterthe beating operation or while beating is in progress. Various amountsof pulverulent cellulose may be added, say from as low as 2% to 5% to ashigh as from 20% to 50%, based on fiber, depending upon thecharacteristics desired in the finished paper. The pulverulent cellulosemay be of a definite particle size, such as obtained from a gradingoperation, or an aggregation of particles of various sizes, such as ispresent in an ungraded batch, or a synthesis of particles of two or moredefinite degrees of fineness. Preferably, the addition of thepulverulent cellulose is made after the beating operation and after ithas been passed through a Jordan or other refining engine, if the beatenstock is subjected to refining. The addition of the powdered celluloseat this stage of stock treatment avoids the possibility of thepulverulent cellulose undergoing hydration or gelat-. inization as aresult of heating or grinding action. Preferably, the powdered celluloseis added in the form of an aqueous milk or slurry, in which conditionformation of clumps or aggregates in the stock .does not take place,particularly when a small amount of hydrophilic colloid such as starch,glue, gelatine, or soap, is present in the water used as a suspensionmedium. Ihe hydrophilic colloid further tends to keep the powder insuspension, so that it does not tend to settle out in the beater engineand vats in which the finished stock is handled on its way to the papermachine. When papers having ink resistance are being produced ratherthan so-called waterleaf papers, not only may the main charge of pulp inthe beater engine be sized as usual, as with rosin size, but thepulverulent cellulose in the form of a slurry may be similarly sizedbefore being added to the pulp in the beater engine. Rather than beingprecipitated on the pulverulent cellulose before it is added to thecharged beater engine, the rosin size may be maintained in solublecondition in the slurry of pulverulent cellulose until the slurry isadded to the beater charge, in which case the rosin size, being a soap,tends to keep the powder free from clumps or aggregates until it isdistributed through the fiber stock, whereupon it may be precipitated asusual with alum on the stock.

The principles of the present invention are applicable in themanufacture of composite or multi-ply papers, in which case the stockused for the inner plies may be highly beaten, so that such inner plieswill have high strength, whereas the outer plies may either be lightlyor well beaten and contain sufiicient pulverulent cellulose so that theresulting multi-ply sheet will be opaque. In such case, the outer pliesshould contain a lar e proportion of powdered cellulose, which, 1naddition to imparting opacity, will give the finished sheet a velvetyfeel quite different from the harsh feel of papers made from highlygelatinized stock. For instance, the furnish for the outer plies may bemade up of a mixture of, say, 50% of fiber and 50% powdered cellulose,and in some instances small quantities of such material as starch, glue,or casein. Or, in some instances, the

.1 pulverulent cellulose may be desirable as a constituent of one ormore of the inner plies of a multi-ply sheet produced as on amultiple-cylinder machine. For example, the multi-ply sheet may be onecomprising inner plies containing suificient pulverulent cellulose toimpart bulk and softness thereto and outer plies made of well-beatenstock to give a comparatively dense, hard surface,the sheet as a wholehaving more or less compressibility and good ink resistance. If desired,the powdered cellulose may be used as the covering element incompositions intended for coating papers, along with glue, casein,gelatine, or other adhesives such as employed in'such compositions, inwhich case the composition may be applied by the use of brushes, kissingrolls, or the other instrumentalities customarily used in themanufacture of coated papers. The coated prodnot is characterized by itslower gloss, higher opacity, and greater flexibility than paper whichhas been coated with a composition in which a mineral color has beenemployed as the covering element.

If desired, the pulverized cellulose may be used together with mineralpowders such as barium sulphate, calcium carbonate, clay, talc, etc., inthe production of filled and/or coated papers as hereinbefore described.The mineral powder is preferably mixed with the fiber from which thepulverulent cellulose is to be prepared, as the mineral owderfacilitates the pulverization of the fi er and the pulverizing operationserves to effect an intimate and uniform mixture of the two filler tothe fiber.

The powdered cellulose-to be used in a given paper product may bederived from a fiber different from that used to form the body of thepaper, but in the production of high grade papers in which new rags or apure white wood pulp of high alpha cellulose content is employed, it ispreferable that the cellulose powder be derived from a pure white fiberhaving the same characteristics as that of the fiber used in the body ofthe paper, in order to ensure a stable or permanent product, i. e., onewhich will stand up against or resist the effects of time, heat, light,and air. The powdered cellulose may,

however, be used in other kinds of paper, 3

such as those made from sulphite or kraft pulp and intended formanufacture into books or magazines, wrappers, bags, towels, etc., inwhich case the pulverized cellulose may be derived from a source quitedifferent from that represented by the fiber in the body of the paper.Papers containing pulverulent cellulose and made as hereinbeforedescribed may be subjected to further treatment of a mechanical sort,such as calendering, or of a chemical sort, such as vulcanization orparchmentization, in which latter case the paper need not containmineral fillers which impair the function of the chemical solutions usedin the treatment.

While I. have hereinbefore described the u production of paper productscontaining pulverulent cellulose, the present invention comprehends acomposition comprising cellulose fiber in a beaten or unbeatencondition, containing pulverulent cellulose such as may be marketed bythe pulp manufacturer to the paper manufacturer. That is to say, a woodpulp manufacturer may, in accordance with the present invention,incorporate into the 1 wood pulp being marketed in bulk from or in theform of so-called drier sheets the desired amount of pulverulentcellulose, s( that the paper manufacturer need not go to the bot-her ofeven handling the pulverulent cellulose.

By the term cellulose or cellulose fiber as used in the appended claims,I mean cellulosic material which is largely free from noncellulosicmatter such as lignin, resins, etc.,

with which a raw cellulosic material such as wood is associated. I amaware of the fact that it has been proposed to use comminuted wood, suchas sawdust or wood flour, in the manufacture of cheap papers or boards,but the presence of such material in papers is accompanied by a rapidyellowing-and deterioration of the paper owing to the instability ofsuch material under atmospheric conditions.

The use of a pure white pulp as hereinbefore described is characterizedby its high covering power and its capability of being a significantingredient in papers having excellent physical characteristics,including strength, tear resistance, and folding endurance.

I claim:

1. A paper possessed of stability against ageing in the atmosphere andcontaining a stable, powdered cellulose, said powdered cellulose beingderived from cellulose fiber practically free from non-cellulosic mattersuch as lignin and resin.

2. A paper possessed of stability against ageing in the atmosphere andfilled with a stable, mechanically powdered cellulose, said powderedcellulose being derived from cellulose fiber practically free fromnon-cellulosic matter such as lignin and resin.

3. A paper filled and coated with powdered cellulose, said powderedcellulose being derived from cellulose fiber practically free fromnon-cellulosic matter such as lignin and resin.

4. A paper coated with powdered cellulose, said powdered cellulose beingderived from cellulose fiber practically free from non-cellulosic mattersuch as lignin and resin.

5. A paper containing powdered cellulose and a mineral powder, saidpowdered cellulose being derived from cellulose fiber practically freefrom non-cellulosic matter such as lignin and resin.

6. A paper filled with powdered cellulose and a mineral powder, saidpowdered cellulose being derived from cellulose fiber practically freefrom non-cellulosic matter such as lignin and resin.

7. A paper possessed of stability against ageing in the atmosphere andcomprising highly gelatinized cellulose fibers and a stable, powderedcellulose, said powdered cellulose being derived from cellulose fiberpractically free from non-cellulosic matter such as lignin and resin.

8. A paper comprising a high alpha cellulose fiber and containingmechanically pulverized similar fiber.

9. A process which comprises pulverizing preliberated cellulose fiber ofthe. character of chemical wood pulp along with a mineral material.

10. A process which comprises mechanically pulverizing preliberatedcellulose fiber of the character of chemical wood pulp, incorporating itinto a papermaking stock, and forming the stock into paper.

11. A process which comprises pulverizing preliberated cellulose fiberof the character of chemical wood pulp, incorporating into a beatenpapermaking stock, and forming the stock into paper.

12. A process which comprises pulverizing preliberated cellulose fiberof the character of chemical wood pulp, forming an aqueous suspension ofthe powder, incorporating the suspension into papermaking stock, andforming the stock into paper. 7

13. A chemical Wood pulp paper containing powdered, preliberatedchemical wood pu p.

14. A chemical wood pulp paper containing similar preliberated wood pulpfibers in powdered condition.

15. A paper comprising wood pulp fibers of high alpha cellulose contentand similar powdered fibers.

16. A process which comprises adding to papermaking stock an aqueousslurry of both cellulose powder and a hydrophilic colloid, and forminginto paper.

.17. process which comprises adding to papermaking stock an aqueousslurry of both cellulose powder and rosin size, and forming into paper.

18. A process which comprises adding to papermaking stock containingrosin size an aqueous slurry of both cellulose powder and rosin size,adding alum to precipitate the size, and forming into paper.

In testimony whereof I have aflixed my signature.

GEORGE A. RICHTER.

